Disinfection and Sterilization

Disinfection It is the Killing of most microbial forms. Some resistant forms of organisms e.g. bacterial spores, mycobacterium , viruses, fungi may remain viable. Disinfection can achieved by boiling, pasteurization ,UV rays and chemical agents.

Antisepsis (by antiseptics) Inhibition or elimination of microbial forms on the skin or living tissue. We can use chemical agents like ethyl alcohol. It is not suitable for systemic administration. Germicides Germicides are chemical agents. They are used for Killing of microbial forms but spores may remain viable.

Sporicide It is Germicide able to killing bacterial spores. Cleaning It is the removal of visible dust, dirt and foreign material by water and soap. It usually precede disinfection and sterilization . Decontamination It is a general term applied to any procedure by which microorganism are reduced to a level where the equipments is safe for handling.

sterilization Mthods of sterilization Sterilization is the Killing of all living forms of microbes (bacteria, fungi and viruses) Mthods of sterilization I-Heat sterilization (moist or dry) II-Low temperature sterilization III- sterilization by radiation IV- sterilization by Filtration

I-Heat Sterilization A: Moist heat Is the most practical efficient and inexpensive method of sterilization, it can be used in two forms: moist heat and dry heat A: Moist heat Is much more efficient than dry heat, because it kills the microbes by coagulation and denaturing of their enzymes and structural protein.

a-Moist heat at a temperature below 100oC An example is pasteurization of milk by heat at either 63oC for 30min or at 72oC for 20sec and immediately cooling to below 10oC. Pasteurization can destroy all non- spore forming pathogens. b- Moist heat at a temperature of 100oC (boiling) Boiling at 100oC for 20Min. to kill all vegetative bacteria and hepatitis B virus but not all bacterial spore . This method may be used for disinfection of surgical equipment).

c- Moist heat at a temperature above 100oC (autoclave) The sterilizing agent is saturated water steam under high pressure. Equipment used called: Autoclave Saturated steam should be free from air. At 2bar (atmospheric pressureX2), the temperature is 121oC and strilization time is 20-30 min At 3bar the temperature is 134oC and sterilization time 3-6min

The autoclave is used for sterilization of culture media, surgical instruments, dressings, gowns, cotton, gauze. Advantages of moist heat 1-Steam has high penetrating power. 2--Not toxic 3-Low cost and not time consuming. Disadvantage of moist heat 1- Some items can not withstand the high temperature of steam 2- Not suitable for powder and oils.

B-Dry Heat Methods of dry heat It is kill the microorganisms by destructive oxidation of essential cell constituents it is less efficient than moist heat. Methods of dry heat 1-Incineration used for tratment of dead animals, infectious hospital wastes, surgical dressings, needles. 2-Red heat Exposing wires, loops, points of forceps to flame until become red.

3-Hot air oven Oven is an double walled metal chamber heated by electricity, to a constant temperature Sterilization time and temperature: 2 hr 160oC for 2Hr One hr 170oC. 30 Min at 180oC Hot air oven is used for sterilization of: glassware, ointments, powders, oils, and metallic instruments

II-Low temperature sterilization 1- By Gas Ethylene oxide 450-1200 mg/L at 56oC Time of exposure varies from 3-6 hours. Its Advantage is capability of sterilizing the instruments that cannot be subjected to steam or hot air oven without any damage . Disadvantage is :long duration ,High cost and toxicity. 2-By liquids 1-PERACETIC ACID 0.2% 2-GLUTARALDEHYDE (Cidex) 2%

III-Sterilization by Radiation 1-Gamma rays 2- β-rays (High- energy electrons) These are used for sterilization of Heat sensitive items like: Prepacked disposable plastic items like plastic syringe ,catheters ,gloves, surgical suture, IV sets and plastic Petri dishes.

3-Ultra Violet light It is present in sun rays It is produced artificially by mercury lamps It has weak penetrating power It is used to reduce the number of bacteria in air and for surface disinfection in certain area e.g. operation room , lab safety cabinet.

IV-Sterilization by Filtration This is the a mechanical exclusion of microorganisms from biological fluids which are sensitive to heat as serum, plasma, hormones, vitamins. Filters used have pore size of less than 0.45um. Viruses and bacteria as mycoplasma pass through filters